NavList:

   

Reply

Bill,
My main source was being taught(made aware of)this in classes when I studied
to sit for my ABS exam and later my 3rd mate exam.It was shown to me while
still an ABS by more than 1 officer in actual situations while plying
oceanic waters.It has served me well(as a rule of thumb)over the course of
my sea going career.There are many veriables.Some of the resulting
calculations get complex.As when the officer/helmsman have to hold the ship
on track and calculate what I mentioned in the origonal post.Wind
currents,leeway,oceanic currents,bow shear,screw torgue, screw slip and
other variables must be vectored to obtain the desired corrections to stay
close to the trackline.When engaged in commerce shipping time is money and
money is time.So,getting this right is important as the captian or 1st
officer wouldn't be pleased to find the vessel is x nm off the track line at
the end of a watch,thus taking longer to get the cargo into port(it could be
bad enough that the vessel would miss the correct tide and have to ride it
out outside the harbor and enter the harbor on the next tide).Bad JuJu for
the OOW if this happens!
Some one(on this list)once mentioned that I must keep good or exceptional
DRs when we were discussing some topic.Damn right I did!I didn't like
getting chewed out by my superior officers for mistakes!
This is a great rule of thumb and is suprisingly accurate when applied.
There are a few books that study this and give examples but I've never seen
it outside of a book not geared for the professional.
"The Merchant Marine Officer's Handbook" 4th or 5th edition devotes space to
it in the chapters dealing with shiphandling and pilotting.I haven't seen a
6th edition yet.
Other than that one book perhaps in other marine teaching institution's
sylabus as that is where I was 1st exposed to it.


Doug

I've read on the subject in several different texts but had little blue
water opportunity to actually try it.  Some add variables such as fetch,
velocity, and how long the wind has been coming from the same direction
(minimum 12 hrs?) to questimate the velocity of the current and how far off
the wind direction it is shifted (up to 45d) by the Coriolis Effect.
Wondered what your source(s) is, and if it/they mentions the above fuzzy
variables?

Thanks
Bill

   

Reply